1. Field of the Invention
The invention relates to processes for enzymatically hydrolyzing proteinaceous solutions, particularly to provide organoleptically desirable protein hydrolysate compositions which can be used for dietary purposes and in particular for hospital diets.
2. The Prior Art
It is well known that proteins can be digested with strong acid or alkali or with enzymes and used in diet foods. Hydrolysis of the protein takes place with the subsequent formation of protein fragments, peptides and amino acids. Fragmented protein materials of this type are desirable products for administration to humans and animals with digestive problems. However, the primary problem relative to the adoption of these techniques is the palatability of the product.
Of the known means to hydrolyze protein, enzymatic hydrolysis is preferred since it does not destroy essential amino acids to the extent that they are destroyed by acid or alkaline hydrolysis. However, enzymatic hydrolysis rarely goes to completion and the products of the enzymatic hydrolysis cannot be predicted and frequently the hydrolyzed protein is unsuitable because it contains bitter-tasting peptides. Products of this type to be effective as diets must be organoleptically acceptable. (Dietary Enzymatic Hydrolysates of Protein with Reduced Bitterness, Clegg et al., J. Food Tech. (1974) 9, 21-29).
In U.S. Pat. No. 3,857,966 there is disclosed a method for preparing an egg albumen hydrolysate which does not contain the characteristic egg smell and taste. Egg albumen in a 5% solution (pH 6.3-6.4) is heated to precipitate the protein. After cooling, the precipitate is separated by centrifugation, homogenized in a Waring blender and centrifuged again. The washing step is repeated once more and the washed precipitate is used to make a 5% protein suspension for hydrolysis.
After heating (95.degree.-100.degree. C.) the protein suspension at an alkaline pH (pH 8-9) for about 1 hour, enzymatic hydrolysis is then conducted using a two-stage enzyme system of an alkaline microbial protease in the first stage and a blend of neutral microbial protease and a plant enzyme in the second stage. Similar techniques are indicated in the patent to be applicable to soy protein isolate, whey or whey protein and fish protein.
The pretreatment is a necessary part of the egg albumen hydrolysis procedure since very little hydrolysis can be obtained in a short period of time without it.
U.S. Pat. No. 4,107,334 uses a similar precipitation technique to prepare the functional protein from microbial, or vegetable protein, or whey by hydrolysis. Generally a solution of low solids and protein content is preferably adjusted to a pH of about the isoelectric point of the protein (4-7) and heated until a large proportion of the protein (at least 50%) has been precipitated (for whey protein concentrate--90.degree. C. for 2 minutes).
After washing the protein is hydrolyzed using any acid, neutral or alkaline protease (fungal protease suggested).
The value of a protein hydrolysate in a special diet program depends in large part on the degree of hydrolysis. For instance, for the use of a hydrolysate for patients with digestion problems, at least 80% of the hydrolysate should be in the form of peptides of 500 molecular weight or less and 95% of the hydrolysate should be in the form of peptides of less than 2000 molecular weight. Such an extensive hydrolysis may have the disadvantages of long uneconomical reaction times, organoleptic problems, and biological contamination problems.
Untreated egg albumen only hydrolyzes to a limited extent over a long period of time. Extensive precipitation and purification pretreatment steps are necessary to effectively hydrolyze egg albumen.